This invention relates to a multi-layered thin-film functional device having stacked thin films and magnetoresistance effect element used in a magnetic sensor. In the field of the functional devices such as magnetoresistance effect elements used for magnetic sensors, electronic elements, and so on, there is a powerful stream toward micro-fabrication and high performance. Along with the improvements in vacuum technologies and film-stacking technologies, stacked thin films have come to be often used as functional devices. Conventional technologies of these multi-layered thin-film functional devices are explained below taking a magnetoresistance effect element using a ferromagnetic thin film.
Magnetic resistance effect is the phenomenon that electric resistance changes when a magnetic field is applied to a magnetic body, and it is used in magnetic sensors, magnetic head, or the like. Ferromagnetic thin films of Nixe2x80x94Fe alloys, for example, are employed in magnetoresistance effect elements (MR elements) for reading external magnetic field signals, utilizing their anisotropic magnetoresistance effects (AMR), i.e., the phenomenon that the electric resistance changes depending upon the positional relation between the current flowing in a magnetic body and the magnetic orientation.
Also remarked recently are magnetoresistance effect films made by alternately stacking ferromagnetic layers and non-magnetic layers in cycles of several nm to several decades of nm. In these multi-layered thin films, electric resistance changes depending upon whether the magnetic orientations of ferromagnetic layers opposed to each other via a non-magnetic layer are parallel or not. This phenomenon is called giant magnetoresistance (GMR), and researches are under progress toward the application of this nature, similarly to the anisotropic magnetoresistance effect, in magnetoresistance effect elements (GMR elements) for reading external magnetic signals.
Additionally, large hopes are placed on the giant magnetoresistance effect because it promises a larger change in resistance than the anisotropic magnetoresistance effect also when the film is thin. There are different types of film structures exhibiting giant magnetoresistance effects. Among them, a film structure of one type represented by Fe/Cr artificial lattice films (Phys. Rev. Lett. 61(1988)2472) and Co/Cu artificial lattice films (J. mag. mag. mater. 94(1991)L1), for example, has an anti-ferromagnetic coupling type magnetic interaction between ferromagnetic layers, and changes in resistance are obtained in response to an external magnetic field to change relative directions of magnetic moments between the ferromagnetic. In a film structure of another type represented by CO/Cu/NiFe artificial lattice films (J. Phys. Soc. Jpn. 60(1991)2827), two or more different ferromagnetic layers are used in a multi-layered film made up of a ferromagnetic layer and a non-magnetic layer, and a difference in coercive force of these ferromagnetic layers to change relative directions of magnetic moments between the magnetic layers and thereby obtain changes in resistance in response to an external magnetic field.
Also proposed is a spin valve structure (for example, NiFe/Cu/NiFe/FeMn film (J. Appl. Phys. 69(1991)4774)) having a sandwich film stacking a ferromagnetic layer, non-magnetic layer and ferromagnetic layer and having a weak magnetic interaction among the magnetic layers, in which the resistance can be readily switched by providing an anti-ferromagnetic layer in contact with one of the ferromagnetic layer so that the exchange anisotropy fixes the magnetic moment of the ferromagnetic layer and by changing the magnetic moment of the other ferromagnetic layer in response to an external magnetic field.
As reviewed above, multi-layered thin-film devices made by stacking very thin layers as thin as 100 nm, approximately, have come to be used as magnetoresistance effect elements and other active elements. In these multi-layered thin-film functional devices, characteristics of active elements often vary due to the inter-diffusion of atoms at boundaries between thin-film layers, and thermal stability of their characteristics is an important issue for their practical use.
It is therefore an object of the invention to provide a multi-layered thin-film functional device having an functional layer made by stacking a plurality of thin films, which is improved in thermal stability and long-term reliability by suppressing inter-diffusion of atoms among the thin-film layers in the functional layer.
Another object of the invention is to provide a magnetoresistance effect element which is improved by thermal stability and long-term reliability by suppressing inter-diffusion of atoms at a ferromagnetic layer and a non-magnetic layer in the magnetoresistance effect element.
Another object of the invention is to provide a magnetoresistance effect element having excellent magnetoresistance effect characteristics and other various magnetic characteristics and having excellent thermal resistance by well maintaining the function of an electron reflecting layer made to exist in a spin valve film, effectively preventing adverse influences to magnetic characteristics based thereon, and preventing defective fabrication of the layer itself; provide a method for manufacturing such magnetoresistance effect elements with a good reproducibility; and provide a magnetoresistance effect element stably operable as a magnetic head, for example.
According to the one aspect of the invention, a multi-layered thin-film functional device including a base crystal layer, a crystal growth controlling layer formed on said base crystal layer, and a functional layer made up of a plurality of thin-film layers formed on said crystal growth controlling layer, said crystal growth controlling layer containing a compound of at least one element selected from O, N, C, F, B and S, said base crystal layer having a thickness not thicker than 15 nm, and the roughness of the boundary between said crystal growth controlling layer and said functional layer being not larger than 1.5 nm is provided.
According to the another aspect of the invention, a magnetoresistance effect element having a magnetoresistance effect film which includes a crystal growth controlling layer as one of films therein, characterized in that a roughness along a boundary between films overlying said crystal growth controlling layer is smaller than a roughness along a boundary between films underlying said crystal growth controlling layer is also provided.
The inventors found that the thermal instability was caused by the inter-diffusion of the atoms and that the such a diffusion is enhanced by the bulkiness of the grain size of the layers of the functional device. FIG. 24 schematically shows the bulkiness of the grains. According to the invention, such a bulkiness is prevented by employing the crystal growth controlling layer.
According to the another aspect of the invention, a magnetoresistance effect element comprising a first magnetic layer (free layer) susceptible in magnetization to an external magnetic field, a second magnetic layer (pinned layer) substantially pinned in magnetization, and a non-magnetic intermediate layer interposed between said first magnetic layer and said second magnetic layer, characterized in further comprising a metal barrier layer provided adjacent to said first magnetic layer, and a fourth layer (electron reflecting layer) located adjacent to said metal barrier layer and containing at least one selected from oxides, nitrides, carbides, fluorides, chlorides, sulfides and borides is also provided.
According to the another aspect of the invention, a magnetoresistance effect element comprising a first magnetic layer susceptible in magnetization to an external magnetic field, a second magnetic layer substantially pinned in magnetization, and a non-magnetic intermediate layer interposed between said first magnetic layer and said second magnetic layer, said second magnetic layer including a third layer (electron reflecting layer) containing at least one selected from oxides, nitrides, carbides, fluorides, chlorides, sulfides and borides is also provided.
According to the another aspect of the invention, a magnetoresistance effect element comprising a second magnetic layer substantially pinned in magnetization, a non-magnetic intermediate layer formed on top surface of said second magnetic layer, a first magnetic layer formed on top surface of said non-magnetic layer and susceptible in magnetization to an external magnetic field, and a third layer formed on top surface of said first magnetic layer and containing at least one selected from oxides, nitrides, carbides, fluorides, chlorides, sulfides and borides is also provided.
According to the another aspect of the invention, a magnetoresistance effect element comprising a magnetic metal base layer, a metal barrier layer formed on said magnetic metal base layer, a first magnetic layer made on said metal barrier layer and susceptible in magnetization to an external magnetic field, a non-magnetic intermediate layer made on said first magnetic layer, and a second magnetic layer made on said non-magnetic intermediate layer and substantially pinned in magnetization is also provided.
According to the another aspect of the invention, a method for manufacturing a magnetoresistance effect element which includes a first magnetic layer susceptible in magnetization to an external magnetic field, a second magnetic layer substantially pinned in magnetization, and a non-magnetic intermediate layer interposed between said first magnetic layer and said second magnetic layer, and a electron reflecting layer located closer to at least one of said first and second magnetic layers or inside one of said first and second magnetic layers and including a metal compound, comprising the steps of making said electron reflecting layer while irradiating at least one of radicals, ozone and light.
According to the another aspect of the invention, a fabricating machine for manufacturing a magnetoresistance effect element which includes a first magnetic layer susceptible in magnetization to an external magnetic field, a second magnetic layer substantially pinned in magnetization, and a non-magnetic intermediate layer interposed between said first magnetic layer and said second magnetic layer, and a electron reflecting layer located closer to at least one of said first and second magnetic layers or inside one of said first and second magnetic layers and including a metal compound, comprising the means for making said electron reflecting layer while irradiating at least one of radicals, ozone and light.
Electric resistance of a multi-layered film of two different kinds of metals varies with the inter-diffusion of atoms at the boundary. The inter-diffusion of atoms at the boundary between a magnetic layer and a non-magnetic layer also causes a decrease in magnetic volume of the magnetic layer and hence decreases the magnitude of the magnetization. On the other hand, in elements utilizing the giant magnetoresistance effect, spin-dependent scattering of electrons along the boundary between a ferromagnetic layer and a non-magnetic layer is essentially important for the magnetoresistance effect. In these GMR elements, inter-diffusion of atoms at the boundary between the ferromagnetic layer and the non-magnetic layer directly affects the magnetoresistance changing ratio, and the magnetoresistance changing ratio is significantly decreased by inter-diffusion of atoms.
As discussed above, multi-layered thin-film functional devices stacking very thin layers as thin as approximately 100 nm involve the problem that characteristics of the active element are liable to vary due to inter-diffusion of atoms at the boundary between the thin-film layers. Especially in GMR elements, inter-diffusion of atoms at the boundary of a ferromagnetic layer and a non-magnetic layer largely decrease the magnetoresistance changing ratio.
The multi-layered thin-film functional device and the magnetoresistance effect element according to the invention alleviate inter-diffusion of atoms between thin-film layers in the functional layer such as magnetoresistance effect film, therefore greatly improve the thermal stability, and increase the long-term reliability. Especially the magnetoresistance effect film can realize thermal stability excellent in MR changing ratio.
Additionally, the invention can maintain the function of a diffusion preventing electron reflection layer provided in a multi-layered film such as spin valve film and can thereby remove adverse affection to the magnetic characteristics. Therefore, the invention can provide a magnetoresistance effect element having good magnetoresistance effect characteristics and other various magnetic characteristics, and excellent in thermal resistance.
Furthermore, according to the invention, since uniform and dense diffusion preventing electron reflection layers with smooth boundaries and large mirror reflection effects can be made with a good reproducibility, the invention can provide a manufacturing method capable of stably manufacturing high-performance magnetoresistance effect elements excellent in thermal.